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Monday, November 28, 2016

The margins
of carbonate platforms can be steep, and even form vertical walls. This
contribution from Ginsburg et al. uses submersible observations of
geomorphology, biota, and sediment (illustrated by striking hand-drawn figures)
of one of the steepest margins, in Tongue of The Ocean (TOTO), a deep-water
embayment in the Bahamas, to explore the growth potential of such
margins. The results revealed a “luxurious reef-building community”
including corals, sponges, and Halimeda present even on near-vertical
walls; these organisms were interpreted to “produce slow but significant outward
accretion of the wall.” And so it turns out that beyond just being another
brick in the wall, organisms are important in building these
features.

Tuesday, November 22, 2016

The origins
of red beds have fascinated geoscientists for generations. In this
contribution, Picard examined the Red Peak Member of the Chugwater Formation (Triassic) in
west-central Wyoming, a thick succession of red sandstone and siltstone. Coupling
field sedimentologic observations, petrography, X-ray diffraction, and well log
analysis, the study focuses on the ubiquitous siltstone, rather than the
sandstone units. The data led Picard to suggest that the climate was warm
to hot and semi-arid to arid, but he ended with the penetrative suggestion that
“Further study of [redbed] siltstones is urged.” Many geologists who favor
gingers have gladly followed his advice.

Wednesday, November 16, 2016

As study of
the deep-water fans deposits has advanced to progressively finer scales, debate
regarding the nature and origin of stacking patterns has become refined. To
quantitatively test conceptual models, Terlaky and others statistically analyze
stacking patterns of stratal elements in the Proterozoic Upper Kaza Group
(Windermere Supergroup, Cariboo Mountains, southern Canadian Cordillera) by
Markov-chain analysis, an under-utilized tool in deep-water sedimentologic
research. The results of the analysis shows that the stacking pattern in this
passive-margin sedimentary pile is statistically non-random, and is more
heterogeneous than would be expected in a random distribution. These
observations form the basis for a conceptual model for lobe development driven
by splay deposition and frequent avulsion. Beyond showing the utility of
the tool, the results are interpreted to be significant for reservoir
characterization in similar passive-margin settings, providing analogs and data
on thicknesses, volumes, and connectivity of stratal elements and reservoir
bodies.

Thursday, November 10, 2016

Regional sequence stratigraphic correlations of
tidally-modified deltaic deposits are very difficult because of the spatial and
temporal variability in facies distribution and resultant complex stacking
patterns. To understand these types of systems, Burton and othersexamine
the sedimentology and stratigraphy of the Loyd and Sego sandstones across the
Uinta–Piceance basins by integrating outcrop and subsurface (core and log)
data. The data lead to a sequence stratigraphic correlation and associated
maps, from which they interpret controls on depositional processes over time. These
types of well-constrained analogs can provide perspectives for enhanced
interpretation of similar deposits in basins where subsurface data are sparse.

Monday, November 7, 2016

Facies patterns of
many carbonate depositional systems are described as complex. In this
contribution from 10 years ago, Beavington-Penney et al.describe
another end member—the extremely homogenous (even boring) succession of the
middle Eocene Seeb Formation in Oman. Outcrop description, petrographic
characterization, and biofacies analysis reveal a ~250 m thick succession of
nodular, indistinctly bedded shallow-subtidal sediment, which is largely
acyclic. These results were interpreted to highlight the role of
bioturbation and rhizoturbation in homogenizing the succession, and destroying
evidence for surfaces and horizons that represent “missing time.” The data
and interpretations suggest that slow accumulation rates and intense sediment
re-working drive homogeneity, and that it is not only unpredictability that can be monotonous.

Wednesday, November 2, 2016

The
geochemical attributes of paleosols have been used to estimate
paleoenvironmental and paleoclimatic conditions through much of the
Phanerozoic. Here,Michel et al. use plane-polarized
and cathodoluminescence petrography, electron microprobe, and stable isotope
ratio mass spectrometry observations of paleosols from Permo-Carboniferous
strata of the Lodève Basin, France to evaluate the role of post-depositional
alteration on geochemistry of paleosols. The results illustrate that
macrofeatures within paleosols are retainend and can be used for paleoclimate
reconstruction; however, geochemical signatures are neither reflective of soil
formation nor appropriate to use in paleoclimate reconstruction due to
diagenetic alterations. Yet, the paleosol carbonate cements and matrix clays
preserve information that reflects a complicated calcite-cement stratigraphy
recorded in nodules, and quartz, barite, dolomite, and Fe-rich calcite
cementation. These results emphasize that pedogenic nodules, rhizoliths,
and paleosol matrix should systematically evaluated for diagenetic alteration
prior to applying geochemical based proxies to reconstruct paleoclimate.